JPS5842014B2 - Polyamide film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is made of polycapramide or polyhexamethylene adipamide, and has excellent physical properties such as excellent transparency, pinhole resistance, gun barrier properties, and oil resistance, as well as good mechanical properties. The present invention relates to a method for stably producing a uniform biaxially stretched film having the following properties by a sequential stretching method.

More specifically, a boria □ film made of substantially amorphous polycapramide, polyhexamethylene adipamide, or a copolymer or mixture thereof with a relative viscosity of 3.5 or more is first heated at 70°. After stretching 2.0 to 4.5 times in the direction perpendicular to the extrusion direction (hereinafter referred to as the transverse direction) at C to 180°C, it was stretched to 1000°C at 70 to 180°C
The film was stretched in the extrusion direction (hereinafter referred to as the machine direction) at a stretching speed of 0.00%/min or more at a stretching ratio of 2.0 to 6.0 times until the necking part disappeared and a uniform film was obtained. Accordingly, a film having the above-mentioned good properties is produced.

The relative viscosity referred to here means 25°C using 96% sulfuric acid.
refers to the relative viscosity of the polymer measured at
A film obtained from a polymer with this value of 3.5 or more (
The use of the original film (original film) has the important advantage that the stability during longitudinal stretching is significantly improved, and that a biaxially stretched film with balanced properties in the longitudinal and lateral directions can be easily produced.

The present invention will be explained in more detail below.

Conventionally, as an industrially advantageous biaxial stretching method for thermoplastic resin films, a sequential biaxial stretching method has often been used, as typified by polyester.

However, when successive biaxial stretching is attempted in a boria □ board, the subsequent stretching becomes uneven or even breaks due to the molecular alignment and strong intermolecular hydrogen bonds generated in the first stretching.

For this reason, it is extremely difficult to obtain a uniform polyamide film by this method, and it has been accepted as common knowledge in the art that polyamide films are not suitable for two-step stretching.

Regarding this point, the invention disclosed in Japanese Patent Publication No. 37-2195 makes it possible to perform sequential biaxial stretching by adding a plasticizer to the polyamide in order to improve the stretchability.

However, the film produced by this method has problems in terms of practicality, such as deterioration in film properties caused by the use of plasticity and other drawbacks.

Furthermore, in Japanese Patent Publication No. 43-9399, recognizing that it is extremely difficult to obtain a uniform boria □ doped film by successive biaxial stretching, it is proposed that a uniform biaxial film be obtained by spatially simultaneous biaxial stretching in both the vertical and horizontal directions. A method of obtaining the film is proposed.

This method is the only biaxial stretching method for boria □ film that is used industrially, but it can only be carried out using a complicated simultaneous biaxial stretching machine, and as is well known, there is a great deal of freedom in setting conditions. There are problems such as a small width, a poor yield due to unevenly stretched wide ends, and a tendency to tear because the strip edge that is not gripped by the grip is overstretched. .

On the other hand, Japanese Patent Publication No. 47-3195 discloses a stretching method based on a sequential biaxial stretching method as an improvement of the above simultaneous biaxial stretching method, in which the roll conditions etc. during the initial longitudinal stretching are changed. Strictly defined methods allow for subsequent stretching in the transverse direction, and a sequential biaxial stretching method from longitudinal to transverse has been proposed.

However, even with this method, the conditions are extremely narrow, and the degree of freedom for uniform and stable lateral stretching is extremely small.

The inventors of the present invention have carefully considered the shortcomings of these conventional techniques and have conducted intensive studies on a method for sequential biaxial stretching of polyamide films that has high productivity and a wide range of optimal conditions. 70 pieces of regular polyamide film
2.0 to 4.5 in the lateral direction in the temperature range of ~180℃
Stretched twice as much, then 1x in the longitudinal direction at 70-180°C.
2.0 to 6 with a high stretching speed of 00000%/min or more and a uniform film with the necking disappearing.
．． It was discovered that a Boria□Don axially stretched film satisfying these requirements could only be obtained by stretching at a stretching ratio of 0 times, followed by heat setting if necessary. did.

Subsequently, the present inventors further investigated the above-mentioned stretching method in detail using polyamide films such as polycapramide and polyhexamethylene adipamide, and found that by increasing the degree of polymerization of these films, the stability of stretching was significantly improved. At the same time, there is a tendency that the magnification at which the necking phenomenon that occurs during the second stage longitudinal stretching when sequentially biaxially stretching a polyamide film from the transverse direction to the longitudinal direction disappears tends to decrease. The present inventors have discovered the extremely interesting fact that a uniform film can be easily obtained even by stretching the film, leading to the creation of the present invention.

In other words, polymers with a relatively low degree of polymerization, such as those conventionally used for fibers, specifically 96%.
Even with films obtained from polymers with a relative viscosity of less than 3.5, measured at 25° C. using sulfuric acid,
Sufficiently uniform sequential biaxial stretching is possible by the transverse to longitudinal stretching method shown in Japanese Patent Application No. 49-123452, but the second stage longitudinal stretching is carried out at a high speed of 100,000%/min or more. Because it is necessary to carry out longitudinal stretching, fractures tend to occur during this longitudinal stretching, and especially near the magnification where necking disappears, the stress increases rapidly and the frequency of fractures increases; It wasn't always completely satisfying.

The longitudinal stretching speed mentioned here means that the feeding speed of the film is V1 (m7 minutes), the take-up speed is V2 (m7 minutes), the stretching area where the film is actually stretched is a (m), and the stretching ratio is X. It is shown by the following formula.

Stretching speed (%/min) To obtain a high stretching speed, either increase the stretching ratio or
It is possible to increase (1) and (2) or decrease a, but in either case, due to such a high stretching speed, sudden stress is applied to the film during longitudinal stretching. At the same time, since the initial stretching is necking stretching, local stress concentration occurs, and as a result, it cannot be said that the stretching stability at this stage is necessarily sufficient for low polymerization degree films.

On the other hand, polyamide films with a relative viscosity of around 3.5 or higher have a significantly lower frequency of breakage even if sudden stress concentration occurs under such high drawing speeds. It has been found that the stability of stretching is dramatically improved.

However, as the degree of polymerization increases, the extrusion pressure during melt film formation increases significantly, making it impossible to increase the output rate. In addition, when obtaining highly polymerized polymers, it is necessary to Since a reaction is required, problems such as thermal deterioration, oxidative deterioration, etc. are likely to occur, and the quality control of the obtained chips must be extremely strict.

Therefore, it is practically desirable to use a polymer having a relative viscosity of 5.0 or less as an industrially advantageous range of polymerization degree.

Detailed results on film relative viscosity and stretching stability are shown in Examples 1 and 2.

A more effective stretching characteristic that occurs in the method of the present invention includes a phenomenon in which the necking disappearing ratio during longitudinal stretching occurs as the degree of polymerization increases.

The necking disappearance magnification referred to here means that when a substantially amorphous polyamide film is sequentially biaxially stretched from horizontal to vertical, the next longitudinal stretching is During stretching, in the low magnification region, the molecules are partially stretched (rearranged) in the longitudinal direction, and are aligned with one-line linking, and then the molecular chains that were aligned in the transverse direction are This refers to the longitudinal stretching magnification at which all the molecular chains to be rearranged by the applied deformation force are completely aligned in the longitudinal direction, and in order to obtain a uniform stretched film, it is necessary to stretch the film beyond this magnification. is necessary.

Also, the magnification at which this necking disappears is
As described in the specification of No. 3452, different values are taken depending on the doubling ratio of the first-stage transverse stretching temperature and the second-stage longitudinal stretching temperature.

To be more specific, when the transverse stretching ratio is specified, the higher the transverse stretching temperature and the higher the next longitudinal stretching temperature, the higher this magnification is.On the other hand, when the transverse stretching temperature and longitudinal stretching temperature are specified The higher the initial transverse stretching ratio, the higher this ratio tends to be.

This phenomenon occurs under conditions where intermolecular forces act strongly during the first stage of transverse stretching and oriented crystallization progresses, or under conditions where the crystallization rate during the second stage of longitudinal stretching is low. When this is done, it is difficult for the molecules to rearrange smoothly;
In other words, this means that the necking disappearing magnification increases, and the same reason can explain the phenomenon in which the longitudinal stretch necking disappearing magnification decreases when the degree of film polymerization is increased.

As the degree of polymerization increases, the crystallization stage due to orientation during transverse stretching becomes smaller and the crystallization speed becomes slower.
Compared to low polymerization degree films, molecular rearrangement during longitudinal stretching is
It is thought that necking disappears at low magnification as a result of smoother operation.

One of the effects of the present invention is that due to such a reduction in necking elimination magnification, it is easier to obtain a film that has properties that are balanced in both the vertical and horizontal directions, or a film that is strengthened in the horizontal direction. It is.

Even if a film with a relatively low degree of polymerization such as a relative viscosity of less than 3.5 is used, an appropriate transverse stretch ratio and longitudinal stretch ratio selected from the conditions shown in Japanese Patent Application No. 123452/1980 can be used. By combining the
Furthermore, it is possible to obtain a biaxially stretched film with a uniform strength in the vertical and horizontal directions, depending on the application, by using the film 1 that is strengthened in the vertical and horizontal directions. When trying to obtain a film that is strong in the transverse direction, it is necessary to make the longitudinal stretch ratio approximately equal to or lower than the transverse stretch ratio, so it is necessary to create a condition in which the necking disappearing ratio is sufficiently small. There arises a need to choose.

Such conditions mean that it is preferable that the transverse stretching temperature and the longitudinal stretching temperature be lower, and that the transverse stretching ratio is lower. However, if the transverse stretching ratio is too low, the thickness existing in the original fabric Not only is the unevenness expanded and it becomes difficult to make the thickness uniform in the transverse direction, but also the effect of stretching on improving mechanical and physical properties is small, making it impossible to obtain a satisfactory film.

Therefore, in order to obtain a sequentially biaxially stretched film that is balanced in both the longitudinal and transverse directions, or is strong in the transverse direction, and has uniformity and mechanical and physical properties sufficient for practical use, both transverse and longitudinal stretching are necessary. Since it was necessary to stretch at a relatively low temperature and increase the magnification to a sufficient extent to obtain a sufficient stretching effect, the stability of stretching tended to worsen.

By increasing the longitudinal stretching temperature, the stability of stretching gradually improves, but as mentioned earlier, it is not sufficiently satisfactory, and moreover, because the necking elimination ratio increases, However, since this tends to result in a film that is rather strengthened, it cannot be said to be particularly advantageous as a method for obtaining a film with balanced properties as described above or a film that is strong in the lateral direction.

As an effect of the present invention, by using a film having a degree of polymerization with a relative viscosity of 3.5 or more, a film for such purposes can be easily obtained with good stability, and it can also be strengthened in the longitudinal direction. It was confirmed that a film obtained by the above method could also be easily and stably obtained.

Note that the stretching conditions for the film with a relative viscosity of 3.5 or more used in the present invention are as described in Japanese Patent Application No. 123452/1983.
Same as the range shown in the specification, the horizontal stretching is 70 to 18
2.0 to 4.5 times at 0°C, 2 times longitudinal stretching at 70 to 180°C
．． A range of 0 to 6.0 times is selected, and the longitudinal stretching speed must also be 100,000%/min or more.

It is also possible to add various additives, such as lubricating agents, antioxidants, matting agents, coloring pigments, etc., to the polyamide film used in the present invention within a range that does not substantially impair its properties. There is nothing wrong with that.

Some examples are listed below to further specifically explain the present invention.

Example 1 The relative viscosity measured at 25°C using 96% sulfuric acid was 3.0. A substantially amorphous film with a thickness of 0.15 mm was obtained from the polycapramide of 3.5.3.9.4.5.

These films were heated at 100°C in the transverse direction using a tenter.
After stretching the film 3 times with , the tenter clip portion was cut out.

The transversely stretched film thus obtained was stretched using a longitudinal stretching device described below.

That is, the 10th and 20th wheels are rotating at a circumferential speed of 5 m/min.
Between the 20th wheel rotating at a circumferential speed of m/min, a diameter of 5
A stretching roll having a diameter of cmφ and a temperature of 140° C. was arranged, and the horizontally stretched film was stretched vertically with a film contact width of 2 cm.

The stretching speed at this time was approximately 1.9 x 105%, and the stretching was uniform.

In this way, films of each degree of polymerization were
Table 1 shows the relationship between the relative viscosity of the film and the number of breaks when longitudinally stretched for a time.

Example 2 Substantially 0.15 mm thick polyhexamethylene adipamide having a relative viscosity of 2.8, 3, 4, 4, 0, 4.5, respectively, measured at 25° C. using 96% sulfuric acid. An amorphous film was obtained.

These films were sequentially biaxially stretched in the transverse direction and in the longitudinal direction under the same conditions as in Example 1 using the bright apparatus.

Similarly, Table 2 shows the relationship between the relative viscosity of the film and the number of breaks when longitudinally stretched for 8 hours.

Example 3 Using the four types of unstretched polyhexamethylene adipamide films shown in Example 2, 100% of the unstretched polyhexamethylene adipamide films in the transverse direction were used in the same apparatus.
After stretching 3.0 times at 0°C, longitudinal stretching was carried out to approximately 1.9X10'
%/min at 140°C.

Table 3 shows the relationship between the relative viscosity of the film and the necking disappearance rate during longitudinal stretching.

Example 4 Relative viscosity measured at 25°C using 96% sulfuric acid is 3.
0.15m thick from polyhexamethylene adipamide
A substantially amorphous film of m was obtained.

This film was placed in a tenter at 80°C for 3
After double stretching, the tenter clip portion was cut out, and this was longitudinally stretched using the same device as in Example 1.

That is, the stretching temperature was 90 DEG C., the 10th direction speed was 8 m/min, and the film was stretched three times as much as the 20th direction to obtain a biaxially stretched film having almost balanced properties.

The longitudinal stretching speed at this time was approximately 1.6×105%/min, and necking disappeared at a longitudinal stretching ratio of 2.7 times.

On the other hand, from polyhexamethylene adipamide with a relative viscosity of 4.5 measured under the same conditions, the same thickness was 0.1.5 mm.
An amorphous film was obtained.

This film was similarly stretched 3 times in the transverse direction at 100°C and then 3 times in the machine direction at 140°C.

The necking elimination ratio at this time was approximately 2.4 times.

Table 4 shows the relationship between the film relative viscosity and the number of breaks when the above two types of films were longitudinally stretched for 8 hours under the respective conditions.

Further, the mechanical properties of the film obtained at this time are shown in Table 5.

Claims (1)

[Claims] 1 First, a substantially amorphous polyamide film (original film) such as polycapramide or polyhexamethylene adipamide having a relative viscosity of 3.5 or more as defined in the text is heated to 70%
2,0 in the direction perpendicular to the extrusion direction in the temperature range ~180℃
In the olden days, the necking part disappeared and a uniform film was obtained by stretching ~4.5 times and then stretching at 70~180°C at a stretching rate of 1000%/min or more in the extrusion direction.
A method for producing a sequentially biaxially stretched film, which comprises stretching at a stretching ratio of 2.0 to 6.0 times, and then heat-treating the film at a temperature range of not less than the second-stage stretching temperature and not more than the melting point, if necessary. .